-> and reduce

(require '[com.stuartsierra.dependency :as dep])

(-> (dep/graph)
  (dep/depend :b :a)   ; "B depends on A"
  (dep/depend :c :b)   ; "C depends on B"
  (dep/depend :c :a)   ; "C depends on A"
  (dep/depend :d :c)
  (dep/topo-sort))

; Some new edges we want to add the the graph.
(def new-edges [[:b :a] [:c :b] [:c :a] [:d :c]])

; dep/depend is cumbersome when you have edge tuples.
(defn add-edge [g e]
  (apply dep/depend g e))

; Add and get topological sorting.
(dep/topo-sort (reduce add-edge (dep/graph) new-edges))

; Rewrite to threading again.
; Note that the (#(...)) trick doesn't play well with
; functions like reduce, map, etc when the function they
; take is written using #(...).
(-> (dep/graph)
  (#(reduce add-edge % new-edges))
  dep/topo-sort)

; Use reduce' instead.
(defn reduce' [x f ys]
  (reduce f x ys))

; Works well with ->.
(-> (dep/graph)
  (reduce' add-edge new-edges)
  (dep/topo-sort))